Evaluating the Effects of the Rill Longitudinal Profile on Flow Resistance Law

In this paper, for the first time, the effect of the longitudinal profile shape of the rill (uniform, concave, and convex) on flow resistance law was studied. The first part of the paper is based on a theoretical equation to estimate the Darcy–Weisbach friction factor f, deduced from the power velocity distribution and rill measurements performed on a plot. At first, the equation to estimate the Γ parameter of the velocity profile was calibrated using all available measurements. Then an analysis of the hydraulic characteristics at reach scale, for comparable values of discharge, was carried out, comparing the different profile shapes. To assess the influence of the rill profile …

Verifiche sperimentali della USLE a scala di bacino in Sicilia

Testing the use of an image-based technique to measure gully erosion at Sparacia experimental area

The first part of this investigation was aimed at testing the use of a three‐dimensional (3D) digital terrain model and a quasi‐tridimensional (2.5D) digital elevation model obtained by a large series of oblique images of eroded channels taken from consumer un‐calibrated and non‐metric cameras. For two closed earth channels having a different sinuosity, the ground measurement of some cross sections by a profilometer (P) was carried out and their real volume was also measured. The comparison among the three methods (3D, 2.5D, and P) pointed out that a limited underestimation of the total volume always occurs and that the 3D method is characterized by the minimum difference between measured a…

Misure dell’erodibilità del suolo a scala di parcella nell’area sperimentale di Sparacia

Effetto della lunghezza della parcella sulla perdita di suolo

Roughness effect on the correction factor of surface velocity for rill flows

Flow velocity is one of the most important hydrodynamic variables for both channelized (rill and gullies) and interrill erosive phenomena. The dye tracer technique to measure surface flow velocity Vs is based on the measurement of the travel time of a tracer needed to cover a known distance. The measured Vs must be corrected to obtain the mean flow velocity V using a factor αv = V/Vs which is generally empirically deduced. The Vs measurement can be influenced by the method applied to time the travel of the dye-tracer and αv can vary in different flow conditions. Experiments were performed by a fixed bed small flume simulating a rill channel for two roughness conditions (sieved soil, gravel)…

Monitoraggio dell'erosione rill nell'area sperimentale di Sparacia

Verifiche sperimentali della USLE a scala di parcella in Sicilia

Processo di efflusso da uno stramazzo a profilo W

Testing a theoretical resistance law for overland flow on a stony hillslope

Overland flow, sediments, and nutrients transported in runoff are important processes involved in soil erosion and water pollution. Modelling transport of sediments and chemicals requires accurate estimates of hydraulic resistance, which is one of the key variables characterizing runoff water depth and velocity. In this paper, a new theoretical power–velocity profile, originally deduced neglecting the impact effect of rainfall, was initially modified for taking into account the effect of rainfall intensity. Then a theoretical flow resistance law was obtained by integration of the new flow velocity distribution. This flow resistance law was tested using field measurements by Nearing for the …

Un criterio per la determinazione della tolleranza della perdita di suolo

Analysis of rill step–pool morphology and its comparison with stream case

In this paper, the morphology of step–pool features is analysed using rill measurements and literature data for streams. Close-range photogrammetry was used to carry out ground measurements on rills with step–pool units, shaped on a plot having slope equal to 14, 15, 22, 24 and 26%. Data were used to compare the relationships between H/L, in which H is the step height and L is the step length, and the mean gradient of the step–pool sequence, Sm, for streams or the slope of the step–pool unit, S, for rills. The relationship of H/L against Sm is widely used to test the occurrence of the maximum flow resistance condition in streams, which is associated with the range 1 ≤ (H/L)/Sm ≤ 2. Further …

Il risalto idraulico tipo B-jump:determinazione delle altezze coniugate

A new expression of the slope length factor to apply USLE-MM at Sparacia experimental area (Southern Italy)

Abstract Predicting soil loss due to water erosion by empirical models is useful to assess the severity of the phenomenon in an area of interest and to predict the effect of alternative soil erosion control practices. The USLE scheme cannot be used at the Sparacia experimental area (Sicily, South Italy) to predict event soil loss per unit plot area, Ae, because experimental data suggest that, generally, Ae does not increase with plot length, λ. The USLE-MM scheme uses the runoff coefficient, QR, as an additional independent variable in order to develop an empirical model allowing prediction of storm soil loss values that do not necessarily increase with λ. According to this model, Ae is exp…

On the variation of the correction factor of surface velocity with the measurement vertical for shallow flows over rough beds

Considering that water flow energy affects the detachment of soil particles, the transport and deposit of the detached particles, the flow velocity is a key variable governing the soil erosion processes at the hillslope scale. The simple dye-tracer technique for measuring mean flow velocity can be applied in non-controlled field applications for which some measurement difficulties (e.g. due to sediment transport, and shallow flows) can occur. The correction factor is usually obtained as the ratio between the mean velocity, deriving from measurements of flow discharge and water depth, and surface velocity. Alternatively, the possibility of using the velocity profile in a given vertical to de…

Rill flow resistance law under sediment transport

Abstract Purpose In this paper, a deduced flow resistance equation for open-channel flow was tested using measurements carried out in mobile bed rills with sediment-laden flows and fixed bed rills. The main aims were to (i) assess the effect of sediment transport on rill flow resistance, and (ii) test the slope-flow velocity relationship in fixed bed rills. Methods The following analysis was developed: (i) a relationship between the Γ function of the velocity profile, the rill slope and the Froude number was calibrated using measurements carried out on fixed bed rills; (ii) the component of Darcy-Weisbach friction factor due to sediment transport was deduced using the corresponding measurem…

Testing slope effect on flow resistance equation for mobile bed rills

In this paper, a recently theoretically deduced rill flow resistance equation, based on a power-velocity profile, is tested experimentally on plots of varying slopes in which mobile bed rills are incised. Initially, measurements of flow velocity, water depth, cross-sectional area, wetted perimeter and bed slope conducted in 106 reaches of rills incised on an experimental plot having a slope of 14% were used to calibrate the flow resistance equation. Then, the relationship between the velocity profile parameter Γ, the channel slope, and the flow Froude number, which was calibrated using the 106 rill reach data, was tested using measurements carried out in plots having slopes of 22% and 9%. …

Testing the use of an image-based technique to measure gully erosion at Sparacia experimental area

The first part of this investigation was aimed at testing the use of a three-dimensional (3D) Digital Terrain Model (DTM) and a quasi-tridimensional (2.5D) Digital Elevation Model (DEM) obtained by a large series of oblique images of eroded channels taken from consumer un-calibrated and non-metric cameras. For two closed earth channels having a different sinuosity the ground measurement of some cross-sections by a profilometer (P) was carried out. The real volume of each channel was also measured by waterproofing it by a plastic film and filling it with a known volume of water. The comparison among the three methods (3D, 2.5D and P) pointed out that a limited underestimation of the total vo…

Testing a new sampler for measuring plot soil loss

Verifica sperimentale del fattore L della USLE-MM nell’area di Sparacia

Testing assumptions and procedures to empirically predict bare plot soil loss in a Mediterranean environment

Empirical prediction of soil erosion has both scientific and practical importance. This investigation tested USLE and USLE-based procedures to predict bare plot soil loss at the Sparacia area, in Sicily. Event soil loss per unit area, Ae, did not vary appreciably with plot length, l, because the decrease in runoff with l was offset by an increase in sediment concentration. Slope steepness, s, had a positive effective on Ae and this result was associated with a runoff coefficient that did not vary appreciably with s and a sediment concentration generally increasing with s. Plot steepness did not have a statistically detectable effect on the calculations of the soil erodibility factor of both…

Experimental investigation of the outflow process over a triangular labyrinth weir

Establishing a soil loss threshold for limiting rilling

In this paper a frequency analysis of event soil loss measurements collected in the period 1999–2012 at the microplots and plots of the Sparacia Experimental Area in Sicily, southern Italy, was developed. The analysis was carried out using the annual maximum soil loss measurements normalized by the mean soil loss measured at a given temporal and spatial scale. The empirical frequency distribution of the normalized variable was well fitted by two Gumbel’s theoretical probability distributions discriminated by a value of the normalized variable equal to 2. This last value discriminates between the relatively low and frequent values of the normalized variable and the high and rare ones. The an…

Determinazione delle altezze coniugate del B-jump su fondo scabro

New technique for measuring water depth in rill channels

Abstract Water erosion is one of the most important soil degradation processes and rill erosion contribution to total soil loss is usually dominant as compared to interrill erosion. Rill erosion modelling requires that rill flow has to be adequately modelled. Flow depths in rills are typically of the order of millimeters to several centimeters and bed topography, characterized by steep slope values, significantly affects flow hydraulics. In this paper, a new technique for measuring the water depth inside a rill channel is proposed and the effects on flow resistance estimate are examined. This technique couples an accurate ground survey of the rill channel, obtained by close-range photogramm…

MEASURING FIELD RILL ERODIBILITY BY A SIMPLIFIED METHOD

Many process-oriented erosion prediction models reproduce rill erosion as affected by site-specific parameters, as for example, rill erodibility, and thus, their practical application requires the measurement of these parameters or their estimate. The aim of this paper was establishing a method for indirectly measuring field rill erodibility. A simple mathematical approach based on a known soil detachment equation and accounting for the rill erosion dynamic process is applied. Field measurements carried out for seven natural rainfall events occurring at the plots of the Sparacia experimental station, southern Italy, are used for indirectly measuring the rill erodibility of the investigated …

A NEW VERSION OF THE USLE-MM FOR PREDICTING BARE PLOT SOIL LOSS AT THE SPARACIA (SOUTH ITALY) EXPERIMENTAL SITE

Improving empirical prediction of plot soil erosion at the event temporal scale has both scientific and practical importance. In this investigation, 492 runoff and soil loss data from plots of different length,  (11 <  < 44 m), and steepness, s (14.9 < s < 26.0%), established at the Sparacia experimental station, in Sicily, south Italy, were used to derive a new version of USLE-MM model, by only assuming a value of one for the topographic length, L, and steepness, S, factors for  = 22 m and s = 9%, respectively. An erosivity index equal to (QREI30)b1, QR and EI30 being the runoff coefficient and the event rainfall erosivity index, respectively, with b1 > 1 was found to be …

Measuring rill erosion at plot scale by a drone-based technology

The traditional direct method (i.e. metric ruler and rillmeter) of monitoring rill erosion at plot scale is time consuming and invasive because it modifies the surface of the rilled area. Measuring rill features using a drone-based technology is considered a non-invasive method allowing a fast field relief. In the experimental Sparacia area a survey by a quadricopter Microdrones md4-200 was carried out, and this relief allowed the generation of a Digital Elevation Model (DEM), with a mesh size of 1 cm and a resolution elevation equal to 2 mm, for three plots (L, G and C) affected by rill erosion. At first for the experimental L plot, which is 44 m long, the rill features were surveyed by a …

Verifica applicativa di tre modelli di stima dell’erosione idrica mediante il concetto di modello fisico

Esperienze sull'efflusso da uno sfioratore a profilo W

Sequent Depth Ratio of a B-Jump

A B-jump is defined as the jump having the toe section located on a positively sloping upstream channel and the roller end on a downstream horizontal channel. This jump often occurs in the stilling basins with a horizontal bottom and located downstream of a steep channel. For a B-jump, a completely theoretical approach is not sufficient to solve the momentum equation and to establish the sequent depth ratio. In this paper, by using the laboratory measurements carried out in this investigation, some available empirical relationships useful for estimating the sequent depth ratio are tested. Then, by using the Π theorem of the dimensional analysis and the incomplete self-similarity theory, a g…

VERIFICA DEL MODELLO CSI PER LA STIMA DELLA PERDITA DI SUOLO

La previsione dell’erosione idrica alla scala temporale del singolo evento riveste particolare interesse dal momento che la perdita di suolo complessiva di un periodo pluriennale è generalmente determinata dagli eventi più rilevanti. Recentemente, utilizzando le misure di perdita di suolo ottenute su parcelle nude installate in tre stazioni sperimentali italiane (Sparacia, in Sicilia; Masse, in Umbria; Caratozzolo, in Calabria), è stato sviluppato un modello empirico, denominato CSI (Central and Southern Italy), per la stima della perdita di suolo alla scala dell’evento. La presente memoria riporta i risultati della verifica di applicabilità del suddetto modello che è stata condotta utilizz…

Twenty years of scientific activity at Sparacia experimental area. Quaderni di Idronomia Montana 33

The main purpose of this booklet is to give to the participants to the Palermo’s Conference of the EU COST ACTION ES1306 - CONNECTING EUROPEAN CONNECTIVITY RESEARCH - CONNECTEUR a general idea of the scientific activity that was carried out in the past 20 years on the basis of the data collected at the Sparacia experimental station for soil erosion measurement, in Sicily, South Italy. The booklet includes a presentation of the experimental site, a description of the applied methods and procedures for measuring soil erosion processes at the Sparacia experimental area, and an illustration of the developed methodologies for predicting soil erosion from plots, small basins, rills and gullies. I…

Measuring rill erosion using structure from motion: A plot experiment

Abstract In this paper the results of a plot experiment on rill erosion are reported. The rill network, manually incised on the soil and further shaped by a clear inflow discharge, was surveyed using the three-dimensional photo-reconstruction (3D-PR) technique which allows to obtain a digital terrain model (DTM) by a large series of oblique images of the channel from consumer un-calibrated and non-metric cameras. The three-dimensional (3D) DTM and the quasi-tridimensional (2.5D) model were generated by Agisoft Photoscan software. For a single rill channel, the reliability of the 3D image-based ground measurements of morphological and hydraulic variables was positively tested by the correspo…

Distribuzioni di probabilità della perdita di suolo parcellare

Processi dissipativi su rampe in pietrame a differente granulometria

Predicting soil loss on moderate slopes using an empirical model for sediment concentration

Summary The objective of this investigation was to estimate event soil loss per unit area from bare plots in central and southern Italy using an empirical model for sediment concentration. The analysis was developed using data collected on bare plots differing in length (11–44 m) and slope (10–26%) at three Italian stations (Masse, Umbria; Caratozzolo, Calabria; Sparacia, Sicily). At first, an analysis was carried out, using the experimental data collected at Sparacia, to establish a relationship between sediment concentration and hydrological variables, such as runoff, rainfall amount and single storm erosion index. Then, an empirical model to estimate plot soil loss as a function of rainf…

Dissipative analogies of step-pool features: From rills to mountain streams

Abstract In this paper the dissipative similarity of step-pool units at different spatial scales ranging from rills to streams is analyzed. This investigation benefits from the latest theoretical advances in open channel flow resistance, high-resolution topography from close-range photogrammetry applied to rill erosion and the availability of published data from literature on step-pool streams. At first, the integration of a power velocity distribution allowed to obtain a theoretically-based expression of Darcy-Weisbach friction factor, in which Γ function and δ exponent of the velocity profile are included. Then this theoretically-deduced flow resistance relationship is calibrated and test…

Predicting maximum annual values of event soil loss by USLE-type models

Abstract Previous experimental investigations showed that a large proportion of total plot soil erosion over a long time period is generally due to relatively few, large storms. Consequently, erosion models able to accurately predict the highest plot soil loss values have practical importance since they could allow to improve the design of soil conservation practices in an area of interest. At present USLE-based models are attractive from a practical point of view, since the input data are generally easy to obtain. The USLE was developed with specific reference to the mean annual temporal scale but it was also applied at the event scale. Other models, such as the USLE-M and the USLE-MM, app…

Sulla determinazione della lunghezza del roller nel caso di risalto tipo B-jump

Misura dell'erosione rill mediante rilievo aereo a bassa quota

Dissipative scaling of step-pool features

Abstract This paper focuses on the dissipative similarity of step-pool units at rill, flume and stream scale. This investigation is carried out using recent advances in open channel flow resistance, applications of close-range photogrammetry to rill erosion, available published data on step-pool features in flumes and streams and a new dataset of measurements in fixed bed step-pool rills. A theoretically-based equation for calculating the Darcy-Weisbach friction factor obtained by integration of a power velocity profile is presented. The scale factor Γ of this power velocity profile, which is included in the flow resistance equation, was previously calibrated (Eq. 10) for mobile bed rills w…

Statistical distribution of soil loss and sediment yield at Sparacia experimental area, Sicily

Abstract An analysis of the statistical distribution of event soil loss was carried out using the data collected in the period 1999–2008 at the microplots and plots of the Sparacia experimental area (Sicily, Italy). For a given microplot size, the analysis allowed to establish that the soil loss frequency distribution was skewed. Using the soil loss normalized by the event mean value, the analysis also showed that the frequency distributions corresponding to different microplot and plot sizes were overlapping, i.e. all distributions were extracted by the same statistical population. The developed analysis allowed to suggest that the soil loss of a given return period can be estimated using …

Testing the USLE-M family of models at the Sparacia experimental site in south Italy

The modified Universal Soil Loss Equation (USLE-M) was empirically deduced by a statistical analysis of the original data set of soil loss measurements used to derive the Universal Soil Loss Equation (USLE). The USLE-M, including the effect of runoffin the event rainfall-runofferosivity factor, is characterized by a better capacity to predict event soil loss. At first, in this paper, using the soil erosion representative variables of USLE-M and the reference condition adopted in the USLE, the dimensional analysis and the self-similarity theory are applied to theoretically deduce a multiplicative equation similar to the USLE-M. Then using the database of the Sparacia experimental site, the a…

Experiments for testing soil texture effects on flow resistance in mobile bed rills

Abstract In this paper a recently theoretically deduced rill flow resistance equation, based on a power-velocity profile, was tested experimentally on plots of varying slopes and soil texture in which mobile bed rills are incised. Measurements of flow velocity, water depth, cross section area, wetted perimeter and bed slope conducted in rill reaches incised on experimental plots, having different slope values (9, 14, 22, 24 and 26%) and soil texture (clay fraction ranging from 42 to 73%), and literature data were used to calibrate the flow resistance equation. In particular, the relationship between the velocity profile parameter Γ, the channel slope, the flow Froude number and texture frac…

Verifica sperimentale di un campionatore per la misura della perdita di suolo

Per la misura di perdita in suolo in parcelle attrezzate è necessaria la stima del peso del materiale solido intercettato nella loro sezione terminale. Nell’area sperimentale di Sparacia, i deflussi torbidi prodotti in seguito ad un evento erosivo vengono convogliati all’interno di vasche di accumulo della capacità di circa 1 m3. Nella memoria per misurare agevolmente il peso di materiale solido eroso da una parcella si propone l’estrazione di campioni rappresentativi della miscela torbida presente in ciascuna vasca facendo uso di un nuovo campionatore appositamente predisposto. La verifica di funzionamento del campionatore è stata condotta effettuando due distinte seri di prove finalizzate…

Testing the Stage-Discharge Relationship in Sloping SMBF Flumes

The Samani, Magallanez, Baiamonte, Ferro (SMBF) flume is a simple and inexpensive instrument for indirect discharge measurement that was originally proposed for use in a horizontal channel and then also applied in sloping channels. The contraction of the flow cross section, aimed at establishing a critical flow condition, is simply obtained by applying two half cylinders to the walls of a rectangular cross section. In this paper a theoretical approach previously proposed for a horizontal SMBF flume is first extended to a sloping SMBF flume and a new stage-discharge relationship is deduced. Then, this equation is experimentally tested using laboratory measurements from literature for differe…

CALIBRAZIONE DI MODELLI USLE-DERIVATI MEDIANTE I MASSIMI ANNUALI DELLA PERDITA DI SUOLO PER EVENTO

Numerosi risultati sperimentali hanno evidenziato che la perdita di suolo pluriennale di una parcella è influenzata apprezzabilmente dall’erosione che si verifica in un numero complessivamente limitato di eventi particolarmente gravosi. Conseguentemente, un intervento di conservazione del suolo calibrato sull’erosione media annua può risultare poco efficace in occasione degli eventi meteorici più significativi dal punto di vista dell’erosione complessiva. La disponibilità di modelli di previsione dell’erosione idrica parcellare in grado di fornire stime accurate dei valori più elevati della perdita di suolo alla scansione del singolo evento erosivo riveste pertanto interesse pratico, potend…

Closure to “Sequent Depth Ratio of a B-Jump” by Francesco Giuseppe Carollo, Vito Ferro, and Vincenzo Pampalone

Rill flow velocity and resistance law: A review

Rills caused by runoff concentration on erodible hillslopes generally have very irregular longitudinal profiles and cross-section shapes. Rill erosion directly depends on the hydraulics of flow within the rills which may differ greatly from that in larger and regular channels like streams or rivers. At first, in this paper, a review of the two different approaches to estimate rill flow velocity, based on flow regime and flow resistance laws, is presented. Recent advances in measurements of rill geometry by the three-dimensional photo-reconstruction (3D-PR) technique, which allows one to obtain a Digital Terrain Model (DTM) by low-altitude aerial and terrestrial photogrammetry, are also disc…

Effects of Biochar Addition on Rill Flow Resistance

The development of rills on a hillslope whose soil is amended by biochar remains a topic to be developed. A theoretical rill flow resistance equation, obtained by the integration of a power velocity distribution, was assessed using available measurements at plot scale with a biochar added soil. The biochar was incorporated and mixed with the arable soil using a biochar content BC of 6 and 12 kg m−2. The developed analysis demonstrated that an accurate estimate of the velocity profile parameter Гv can be obtained by the proposed power equation using an exponent e of the Reynolds number which decreases for increasing BC values. This result pointed out that the increase of biochar content dump…

Flow Resistance in Step-Pool Rills

Rills evolve morphologically, and the adjustment of rill channel geometry to flow affects the relationships among velocity, discharge, and slope. The resistance to flow in step-pool rills is mainly due to form-induced mechanisms and, in comparison, grain resistance is of minor significance. Previous studies on rill flow resistance have been performed exclusively for grainresistance conditions and use a stream flow equation. In this study, a new flow resistance equation, deduced by applying dimensional analysis and self-similarity theory, was applied to rill flow in step-pool channels. First, the incomplete self-similarity hypothesis was used for establishing a power flow velocity profile wh…

Spatial variability of the relationships of runoff and sediment yield with weather types throughout the Mediterranean basin

Este artículo contiene 16 páginas, 6 figuras, 2 tablas.

Effect of plot size on measured soil loss for two Italian experimental sites

The objective of this investigation was to determine empirically the plot width and length effects on runoff volume, Ve, soil loss, Ae, and sediment concentration, Ce, by using data collected, at the temporal scale of the erosive event, on bare plots differing in width (2 to 8 m) and length (11 to 22 m) for two Italian stations (Masse, Umbria; Sparacia, Sicily). Mean results differed by a maximum factor of 1.6 for Ve, 1.8 for Ae and 1.2 for Ce when plots differing in width were compared and by a maximum factor of 1.4 for Ve, 1.2 for Ae and 1.3 for Ce when comparison between plot lengths was conducted. Differences between two plot widths or two plot lengths were not statistically significant…

Simulazione dei deflussi per il bacino sperimentale SPA1 di Sparacia

Dye-tracer technique for rill flows by velocity profile measurements

Abstract Water flow on hillslope soil surface supplies energy which is required to detach soil particles, to transport and deposit sediments, therefore flow velocity is a key variable related to hillslope hydrodinamics of soil erosion processes. Among the different methods available for measuring velocity of shallow interrill and rill flow, the trace technique is widely used. Trace technique is applied by adding a material (salt, magnetic material, water isotope, floating object) and then measuring the speed of the material to travel a known distance from the injection point. When flow velocity is measured using a dye-tracing method, the mean velocity is calculated by multiplying the measur…

Predicting soil loss in central and south Italy with a single USLE-MM model

Purpose: The USLE-MM estimates event normalized plot soil loss, Ae,N, by an erosivity term given by the runoff coefficient, QR, times the single-storm erosion index, EI30, raised to an exponent b1> 1. This modeling scheme is based on an expected power relationship, with an exponent greater than one, between event sediment concentration, Ce, and the EI30/Pe(Pe= rainfall depth) term. In this investigation, carried out at the three experimental sites of Bagnara, Masse, and Sparacia, in Italy; the soundness of the USLE-MM scheme was tested. Materials and methods: A total of 1192 (Ae,N, QREI30) data pairs were used to parameterize the model both locally and considering all sites simultaneously. …

Measuring Rainfall Kinetic Power in Two Sicilian Experimental Areas by Drop-Size Distribution Data

The rainfall kinetic energy, which affects soil erosion processes, can be calculated by the drop-size distribution (DSD) and falling velocity. This study presents the outcomes derived by the DSDs recorded with the same optical disdrometer in two experimental areas, located in Sicily (southern Italy). Specifically, the DSDs were recorded from March 2017 to December 2019 at Sparacia and from June 2006 to April 2014 at Palermo. The aims of this paper are both to compare the DSDs for the two sites and to evaluate the applicability of Gamma theoretical distribution. Moreover, the relations of rainfall kinetic power vs. rainfall intensity are assessed. Differences in DSDs, especially for rainfall…

Estimating flow resistance in steep slope rills

Recent research recognized that the slope of 18% can be used to distinguish between the ‘gentle slope’ case and that of ‘steep slope’ for the detected differences in hydraulic variables (flow depth, velocity, Reynolds number, Froude number) and those representatives of sediment transport (flow transport capacity, actual sediment load). In this paper, using previous measurements carried out in mobile bed rills and flume experiments characterized by steep slopes (i.e., slope greater than or equal to 18%), a theoretical rill flow resistance equation to estimate the Darcy-Weisbach friction factor is tested. The main aim is to deduce a relationship between the velocity profile parameter Γ, the c…

Rilievo e modellazione dell’erosione rill nell’area sperimentale di Sparacia

Comparing two applicative criteria of the soil erosion physical model concept

The physical model represented by a replicated plot has been suggested to be the best possible, unbiased, real world model to predict plot soil erosion. The aim of this investigation was to compare the original applicative criterion of the physical model concept proposed by Nearing with that later suggested by Bagarello et al. The comparison was performed by using three empirical soil erosion models (the Universal Soil Loss Equation [USLE], a modified USLE [USLE-MM], and the Central and Southern Italy [CSI] model) and plot soil loss data collected at the experimental station of Sparacia, in Sicily (southern Italy). The investigation showed that (i) the new criterion was generally more restr…

Il risalto idraulico tipo B-jump:determinazione della lunghezza del roller

A comprehensive analysis of Universal Soil Loss Equation-based models at the Sparacia experimental area

Improving Universal Soil Loss Equation (USLE)‐based models has large interest because simple and reliable analytical tools are necessary in the perspective of a sustainable land management. At first, in this paper, a general definition of the event rainfall‐ runoff erosivity factor for the USLE‐based models, REFₑ = (QR)ᵇ¹(EI₃₀)ᵇ², in which QR is the event runoff coefficient, EI₃₀ is the single‐storm erosion index, and b₁ and b₂ are coefficients, was introduced. The rainfall‐runoff erosivity factors of the USLE (b₁ = 0 and b₂ = 1), USLE‐M (b₁ = b₂ = 1), USLE‐MB (b₁ ≠ 1 and b₂ = 1), USLE‐MR (b₁ = 1 and b₂ ≠ 1), USLE‐MM (b₁ = b₂ ≠ 1), and USLE‐M2 (b₁ ≠ b₂ ≠ 1) can be defined using REFₑ. Then t…

Assessing dye-tracer technique for rill flow velocity measurements

Abstract Rill erosion is considered one of the most important processes affecting soil because of the large amount of soil loss. The rill network acts as sediment source and is able to transport both rill flow-detached particles and those delivered from the interrill areas. Small flow depth in a rill and steep slope values of its bed affect significantly flow hydraulics. When rill flow velocity is measured using a dye-tracing method, the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction factor. The main uncertainty of the dye-tracing technique stands in the relationship between mean and surface flow velocity. In …

Estimating the USLE soil erodibility factor in Sicily, South Italy

The Universal Soil Loss Equation (USLE) is used by professionals and technicians to predict soil loss by water erosion and to establish soil conservation measures. One of the key elements of the USLE is the K factor, which is a measure of the soil erodibility. Given the difficulty in collecting sufficient data to adequately measure K, early in the USLE's history the soil erodibility nomograph method was developed to allow estimation of K based on standard soil properties. Since the nomograph approach was developed based on a small number of soils in the United States, it is necessary for other contexts to check the nomograph's ability to predict the soil's true erodibility. Considering that…

Comparing theoretically supported rainfall-runoff erosivity factors at the Sparacia (South Italy) experimental site

Interpreting rainfall‐runoff erosivity by a process‐oriented scheme allows to conjugate the physical approach to soil loss estimate with the empirical one. Including the effect of runoff in the model permits to distinguish between detachment and transport in the soil erosion process. In this paper, at first, a general definition of the rainfall‐runoff erosivity factor REFe including the power of both event runoff coefficient QR and event rainfall erosivity index EI30 of the Universal Soil Loss Equation (USLE) is proposed. The REFe factor is applicable to all USLE‐based models (USLE, Modified USLE [USLE‐M] and Modified USLE‐M [USLE‐MM]) and it allows to distinguish between purely empirical m…

Flow resistance law under suspended sediment laden conditions

Abstract The uniform flow resistance equation, in the form due to Manning or Darcy-Weisbach, is widely applied to establish the stage-discharge relationship of a river cross-section. The application of this equation, namely the slope-area method, allows to indirectly measure the corresponding river discharge by measurements of bed slope, water level, cross-section area, wetted perimeter and an estimate of channel roughness. In this paper, a recently deduced flow resistance equation for open channel flow was tested during conditions of suspended sediment-laden flow. First, the flow resistance equation was determined by dimensional analysis and by applying the condition of incomplete self-sim…

Monitoraggio dell'erosione rill con rilievo aereo di bassa quota

Flow resistance in mobile bed rills shaped in soils with different texture

Rill erosion is considered one of the most important soil processes because of the large amount of soil loss due to the development of a rill network able to promote an efficient transport of both rill flow-detached particles and those delivered from the inter-rill areas. Rill flow experiments are useful to overcome the gap in rill hydraulics knowledge and to test the reliability of currently applied uniform open channel flow equations for mobile bed rills. In this paper the applicability of a theoretical flow resistance equation, based on a power-velocity profile, to rill channels shaped on soils having different textures was investigated. The measurements (437 runs) of water depth, cross-…

Comment on “Determining soil erodibility for the USLE-MM rainfall erosion model by P.I.A. Kinnell”

Abstract The measurements units of the USLE-MM soil erodibility factor are dependent on the exponent of the erosivity term. This circumstance prevents to compare soil erodibility values of sites differing by the value of this exponent. To overcame this problem, Kinnell (2018) suggested to relate the soil erodibility factor of the USLE-MM with that of USLE-M by a linear relationship with the objective to obtain a soil erodibility factor independent of the power of the erosivity term. The USLE-MB, which is a recently proposed model, has also a soil erodibility factor having measurement units common to USLE modelling environment. Kinnell (2018) also showed that the relationship between the pow…

Comparing flow resistance law for fixed and mobile bed rills

Rills caused by run-off concentration on erodible hillslopes have very irregular profiles and cross-section shapes. Rill erosion directly depends on the hydraulics of flow in the rills, which may differ greatly from hydraulics of flow in larger and regular channels. In this paper, a recently theoretically deduced rill flow resistance equation, based on a power–velocity profile, was tested experimentally on plots of varying slopes (ranging from 9% to 26%) in which mobile and fixed bed rills were incised. Initially, measurements of flow velocity, water depth, cross-section area, wetted perimeter, and bed slope, carried out in 320 reaches of mobile bed rills and in 165 reaches of fixed rills, …

Closure to "New stage-discharge equation for the SMBF flume"

Closure alle discussions sull'articolo "New stage-discharge equation for the SMBF flume"

Scala di efflusso del misuratore a cilindri in canale rettangolare a fondo orizzontale

Disporre di un semplice strumento di misura della portata idrica è fondamentale nelle applicazioni di campo, soprattutto quando il sito di misura risulta essere non facilmente raggiungibile come, ad esempio, nelle stazioni di misura del trasporto solido e di erosione idrica. Il misuratore a cilindri, costituito da due semicilindri ad asse verticale che ostruiscono parzialmente il deflusso liquido, è uno strumento adatto a questo scopo. Nella memoria è presentata una relazione di derivazione teorica della scala delle portate del misuratore a cilindri. In particolare la relazione proposta ha origine dall’equazione di Bernoulli applicata tra la sezione a monte dello strumento, dove si misura i…

Testing a theoretically-based overland flow resistance law by Emmett’s database

Abstract The main aim of this paper was to test a recently theoretically deduced flow resistance equation, based on a power-velocity profile, using a wide database of available measurements carried out in laboratory and field experimental runs with overland flow under simulated rainfall. In comparison with previous calibrations and validations of this theoretically deduced flow resistance equation, the used database by Emmett is characterized by a wide range of rainfall intensities (from 79.2 to 303.5 mm h−1 for laboratory runs and from 178.3 to 215.9 mm h−1 for field investigations) and bed slopes (from 0.33 to 17% for laboratory runs and from 2.9 to 33.2% for field investigations). For th…

VERIFICA DI IPOTESI E PROCEDURE NELLA STIMA EMPIRICA DELLA PERDITA DI SUOLO PARCELLARE IN UN AMBIENTE MEDITERRANEO

La stima dell’erosione idrica mediante approcci empirici ha interesse sia scientifico sia applicativo. Nella presente indagine è stata condotta una verifica di ipotesi e procedure adottate nella USLE e in modelli basati sullo schema USLE per la stima della perdita di suolo da parcelle di suolo nudo nell’area sperimentale di Sparacia, in Sicilia. La perdita di suolo per unità di superficie del singolo evento erosivo, Ae, non è significativamente dipendente dalla lunghezza parcellare, λ, in quanto all’aumentare di λ si riduce il deflusso ma cresce la concentrazione dei sedimenti. I valori di Ae sono crescenti con la pendenza parcellare, s, in quanto il coefficiente di deflusso non varia appre…

Experimental Investigation of the Outflow Process over a Triangular Labyrinth-Weir

In this paper, the outflow process from a sharp-crested triangular labyrinth weir is studied. Applying dimensional analysis and the Π theorem, five dimensionless groups, describing the outflow process, are deduced. The measurements, carried out by using sharp-crested weirs placed in a flume, allowed to establish a dimensionless stage-discharge relation. According to this equation, the flow magnification is affected by either the length magnification ratio or head to one cycle width ratio. The proposed equation, which also satisfies two theoretical boundary conditions, was finally tested by using experimental measurements of different reservoir hydraulic models.

New Stage-Discharge Equation for the SMBF Flume

AbstractFlumes for indirect discharge measurements are widespread and are characterized by a particular shape of the cross section area with various degrees of convergence and subsequent divergence. The flume named Samani, Magallanez, Baiamonte, Ferro (SMBF) is a simple and inexpensive instrument and its channel contraction is obtained by applying two semicylinders to the walls of a rectangular cross section. At first, in this paper a new stage-discharge equation for the SMBF flume is theoretically deduced. Then, this equation is experimentally calibrated using the laboratory measurements from the literature for different values of the contraction ratio. Finally the field measurements carri…

Relationship of Weather Types on the Seasonal and Spatial Variability of Rainfall, Runoff, and Sediment Yield in the Western Mediterranean Basin

Producción Científica

Closure to “Testing the Stage-Discharge Relationship in Sloping SMBF Flumes” by Francesco Giuseppe Carollo and Vincenzo Pampalone

This is the closure to the discussions on the paper "Testing the Stage-Discharge Relationship in Sloping SMBF Flumes".

Slope threshold for overland flow resistance on sandy soils

Recent research on rill flows recognised that an 18% slope can be used to distinguish between ‘gentle’ and ‘steep’ slope cases for the detected differences in hydraulic (flow depth and velocity) and sediment transport variables (flow transport capacity, actual sediment load). The effects of slope on flow velocity, friction factor and transport capacity and their interactions affect process-based erosion modelling. The main aim of this paper is to investigate, for the first time, how slope affects the overland flow resistance on sandy soils, which are characterised by loose particles readily available to be transported and deposited. Using literature measurements carried out in sandy soils f…

Applying the USLE Family of Models at the Sparacia (South Italy) Experimental Site

Soil erosion is a key process to understand the land degradation, and modelling of soil erosion will help to understand the process and to foresee its impacts. The applicability of the Universal Soil Loss Equation (USLE) at event scale is affected by the fact that USLE rainfall erosivity factor does not take into account runoff explicitly. USLE-M and USLE-MM, including the effect of runoff in the event rainfall– runoff erosivity factor, are characterized by a better capacity to predict event soil loss. The specific objectives of this paper were (i) to determine the suitable parameterization of USLE, USLE-M and USLE-MM by using the dataseries of Sparacia experimental site and (ii) to evaluat…

Analisi della geometria idraulica dei rill mediante il data-base del WEPP

Lo sviluppo iniziale dei rill può essere spiegato facendo ricorso alle caratteristiche idrauliche della corrente, quali la velocità media, il numero di Froude e la tensione tangenziale al fondo della corrente. Gli studi già condotti sull’idraulica dei rill hanno permesso di modellizzare la geometria idraulica dei solchi mediante un set di tre equazioni, di forma potenziale, che legano la velocità media u, il tirante medio h e la larghezza del solco w alla portata. L’obiettivo del presente lavoro è stato quello di verificare l’applicabilità delle suddette relazioni potenziali e determinare i relativi coefficienti facendo ricorso alle misure condotte su 33 siti sperimentali che costituiscono …

Testing a theoretical resistance law for overland flow under simulated rainfall with different types of vegetation

Abstract In this paper a recently theoretically deduced flow resistance equation, based on a power-velocity profile, was tested using data collected for overland flow under simulated rainfall carried out in plots with vegetation. The available data were obtained exploring a wide range of rainfall intensities (from 60 to 181 mm h−1) and slopes (from 3.6 to 39.6%), and with four different types of vegetation. The database, including measurements of flow velocity, water depth, cross sectional flow area, wetted perimeter and bed slope, was divided in four datasets (one for each vegetation type), which allowed the calibration of the relationship between the velocity profile parameter Γ, the slop…

Flow resistance of overland flow on a smooth bed under simulated rainfall

In this paper a recently theoretically deduced flow resistance equation, based on a power-velocity profile, was tested using laboratory measurements by Yoon and Wenzel for an overland flow on a smooth bed under rainfall. These measurements of the Darcy-Weisbach friction factor, corresponding to a wide range of the flow Reynolds number (191–5700), were carried out for an overland flow under a simulated rainfall characterized by different intensity values ranging from 13 to 381 mm h−1. At first, the available measured values of flow velocity, water depth, cross sectional area, wetted perimeter and bed slope were used to calibrate the relationship between the velocity profile parameter Γ, the …

Verifica di campo del misuratore a cilindri in un canale rettangolare a fondo orizzontale

Il misuratore a cilindri è un semplice strumento per la determinazione della portata idrica defluente in un canale rettangolare. Lo strumento è costituito da due semicilindri ad asse verticale posti in aderenza alle pareti del canale in modo da determinare un’ostruzione parziale al deflusso. La presenza del restringimento determina un rigurgito a monte dove la misura del tirante consente, mediante un’apposita relazione, di determinare la portata idrica. Nella memoria è presentata una verifica di campo del funzionamento del misuratore a cilindri sito nell’area sperimentale di Sparacia in Sicilia. Il misuratore è inserito in una canaletta a pendenza nulla di 12 cm di larghezza ed è caratteriz…

DEDUZIONE DEL FATTORE L DELLA USLE-MM NELLE PARCELLE SPERIMENTALI DI SPARACIA, IN SICILIA

Nell’indagine è stato messo a punto un modello alternativo per la stima della perdita di suolo parcellare che riproduce anche la relazione tra Ae e  dedotta sperimentalmente. L’approccio utilizzato è quello della USLE-MM, che presuppone l’introduzione, nel set di variabili indipendenti, del coefficiente di deflusso parcellare. Nel modello proposto, il fattore topografico L stabilisce un legame crescente tra Ae e  ma la perdita di suolo dovuta a un fissato evento di pioggia può anche diminuire al crescere della lunghezza allorquando, come verificato sperimentalmente, all’incremento di  risulta associata una diminuzione del deflusso. La verifica del modello proposto con set di dati indipen…

Un nuovo campionatore per la misura della perdita di suolo in parcelle attrezzate

Le misure di perdita di suolo in parcelle attrezzate necessitano la conoscenza del peso del materiale eroso intercettato nella sezione terminale delle parcelle. Nell’area sperimentale di Sparacia attrezzata per la misura della perdita di suolo i deflussi torbidi prodotti in seguito ad un evento erosivo vengono convogliati mediante una grondaia posta a valle di ciascuna parcella all’interno di vasche di accumulo. Per misurare la frazione di materiale solido presente nel volume della sospensione raccolto in dette vasche, si propone l’utilizzo di un nuovo campionatore appositamente predisposto. Esso consiste in un cilindro di ottone, di noto diametro, dotato nella sezione terminale di una valv…

Closure to “New Stage-Discharge Equation for the SMBF Flume” by Francesco Giuseppe Carollo, Costanza Di Stefano, Vito Ferro, and Vincenzo Pampalone

New Solution of Classical Hydraulic Jump

This technical note, applying dimensional analysis and incomplete self-similarity, proposes a new functional relationship for the sequent depth ratio for hydraulic jumps over both smooth and rough horizontal beds. For the smooth bed condition, experimental measurements in the literature were used to calibrate the new relationship. For the rough bed condition the data of a previous investigation were used with new measurements carried out in a rectangular horizontal flume having a gravel bed. Finally, a generalized solution of the sequent depth ratio is proposed.

Practical thresholds to distinguish erosive and rill rainfall events

Abstract In this paper, 1017 rainfall events from 2008 to 2017 are used to identify the rainfall threshold that produces upland erosion at the Masse (central Italy) and Sparacia (southern Italy) experimental stations. The rainfall events are classified into three classes: non-erosive, interrill-only and rill. The threshold values for separating as correctly as possible the erosive rains (case I) and the rill rains (case II) are derived solely from the hyetograph. Each threshold value is obtained by imposing that the long-term erosivity of the events above the threshold is equal to the long-term erosivity of all erosive events (case I) or only rill events (case II). The performances of selec…

ESPERIMENTO DI SIMULAZIONE DELLA FORMAZIONE DEI RILL A SCALA DI PARCELLA

Nella memoria sono riportati i risultati di un esperimento di simulazione della formazione del canale di un rill condotto in una parcella avente una dimensione 2x7 m2 ed una pendenza del 14% realizzata dal Dipartimento di Scienze Agrarie e Forestali dell’Università di Palermo. Una rete di solchi, costituita da due canali principali, è stata, dapprima incisa sul suolo manualmente e successivamente modellata utilizzando una corrente idrica limpida. Sui solchi modellati è stato effettuato, in corrispondenza di 11 sezioni trasversali della parcella, il rilievo delle caratteristiche geometriche e idrauliche utilizzando un profilometro. L’indagine ha inoltre previsto la realizzazione sia di un mo…

Stima dell' erodibilità rill nella'area sperimentale di Sparacia

Studio sperimentale del risalto idraulico su fondo liscio orizzontale e pendente

Assessing an overland flow resistance approach under equilibrium sediment transport conditions

Abstract In this study, for the first time, a theoretically deduced flow resistance equation was tested for an overland flow under equilibrium sediment transport conditions using available experimental data by Liu et al. for five Chinese soils. Initially the relationship among the velocity profile parameter Γ, the channel slope, the flow Reynolds number, the Froude number and the sediment concentration was calibrated using 90 measurements of the available database (Loessial, Cinnamon and Black soil) and tested by other 60 measurements (Red and Purple soil). The results proved that the Darcy–Weisbach friction factor can be accurately estimated by the proposed theoretical approach, with error…

Modeling Rill Erosion at the Sparacia Experimental Area

In this paper the contributions of rill and interrill components to total soil erosion monitored at event scale at the Sparacia experimental area, Southern Italy, were firstly compared and the dominance of the rill component was detected. Then, the reliability of two empirical relationships between the rill length and its eroded volume and among the morphological variables (length, width, depth and volume) describing the channelized process was tested using both direct measurements of rills, carried out for the October 3, 2011 event, and those of ephemeral gullies surveyed on February 2010 at Sparacia. The measurements of rills detected by the direct field relief were compared with those ob…

Measuring Field Rill Erodibility by a Simplified Method

Many process-oriented erosion prediction models reproduce rill erosion as affected by site-specific parameters, as for example, rill erodibility, and thus, their practical application requires the measurement of these parameters or their estimate. The aim of this paper was establishing a method for indirectly measuring field rill erodibility. A simple mathematical approach based on a known soil detachment equation and accounting for the rill erosion dynamic process is applied. Field measurements carried out for seven natural rainfall events occurring at the plots of the Sparacia experimental station, southern Italy, are used for indirectly measuring the rill erodibility of the investigated …

Rill flow resistance law under equilibrium bed‐load transport conditions

In this paper, a recently deduced flow resistance equation for open channel flow was tested under equilibrium bed-load transport conditions in a rill. First, the flow resistance equation was deduced applying dimensional analysis and the incomplete self-similarity condition for the flow velocity distribution. Then, the following steps were carried out for developing the analysis: (a) a relationship (Equation) between the Γ function of the velocity profile, the rill slope, and the Froude number was calibrated by the available measurements by Jiang et al.; (b) a relationship (Equation) between the Γ function, the rill slope, the Shields number, and the Froude number was calibrated by the same …

A Comprehensive Check of Usle-Based Soil Loss Prediction Models at the Sparacia (South Italy) Site

At first, in this paper a general definition of the event rainfall-runoff erosivity factor for the USLE-based models, REFe = (QR)b1(EI30)b2, in which QR is the event runoff coefficient, EI30 is the single-storm erosion index and b1 and b2 are coefficients, was introduced. The rainfall-runoff erosivity factors of the USLE (b1 = 0, b2 = 1), USLE-M (b1 = b2 = 1), USLE-MB (b1 ≠ 1, b2 = 1), USLE-MR (b1 = 1, b2 ≠ 1), USLE-MM (b1 = b2 ≠ 1) and USLE-M2 (b1 ≠ b2 ≠ 1) can be defined using REFe. Then, the different expressions of REFe were simultaneously tested against a dataset of normalized bare plot soil losses, AeN, collected at the Sparacia (south Italy) site. As expected, the poorest AeN predict…

Testing the Universal Soil Loss Equation-MB equation in plots in Central and South Italy

Planning soil conservation strategies requires predictive techniques at event scale because a large percentage of soil loss over a long-time period is due to relatively few large storms. Considering runoff is expected to improve soil loss predictions and allows relation of the process-oriented approach with the empirical one, furthermore, the effects of detachment and transport on soil erosion processes can be distinguished by a runoff component. In this paper, the empirical model USLE-MB (USLE-M based), including a rainfall-runoff erosivity factor in which the event rainfall erosivity index EI30 of the Universal Soil Loss Equation (USLE) multiplies the runoff coefficient QR raised to an ex…

Using plot soil loss distribution for soil conservation design

Abstract Soil conservation design is generally based on the estimation of average annual soil loss but it should be developed taking into account storms of a given return period. However, use of frequency analysis in soil erosion studies is relatively limited. In this paper, an investigation on statistical distribution of soil loss measurements was firstly carried out using a relatively high number of simultaneously operating plots of different lengths, λ (11, 22, 33 and 44 m) at the experimental station of Sparacia (southern Italy). Using a simple normalization technique, the analysis showed that the probability distribution of the normalized soil loss is independent of both the scale leng…

Sul dimensionamento delle rampe in pietrame

Verifica del concetto di modello fisico in due stazioni di misura dell’erosione parcellare

A modified applicative criterion of the physical model concept for evaluating plot soil erosion predictions

Abstract In this paper, the physical model concept by Nearing (1998. Catena 32: 15–22) was assessed. Soil loss data collected on plots of different  widths (2–8 m), lengths (11–44 m) and steepnesses (14.9–26.0%), equipped in south and central Italy, were used. Differences in width between plots of given length and steepness determined a lower data correlation and more deviation of the fitted regression line from the identity one. A coefficient of determination between measured, M , and predicted, P , soil losses of 0.77 was representative of the best-case prediction scenario, according to Nearing (1998). The relative differences, Rdiff  = ( P − M ) / ( P + M ), decreased in absolute value a…

Rilievo e modellazione della rill erosion nell'area di Sparacia

Nella presente indagine, l’applicabilità sia delle relazioni che caratterizzano morfologicamente i rill di Sparacia sia di quelle che ne caratterizzano la geometria idraulica viene testata utilizzando nuove misure condotte in occasione dell’evento del 3 Ottobre 2011. Le suddette misure sono state effettuate su una parcella in cui sono stati rilevati 19 rill e 231 sezioni trasversali. Il confronto delle nuove misure con la relazione lunghezza-volume e con quella dedotta teoricamente sulla base dell’analisi dimensionale, entrambe calibrate con i dati rilevati in precedenti eventi, ha confermato l’applicabilità delle suddette espressioni.

Sequent depth ratio of B-jumps on smooth and rough beds

A hydraulic B-jump has the toe section located on a positively sloping upstream channel and the roller end on a downstream horizontal channel. This paper analyses the B-jump on a rough bed, such as at the transition from a block ramp to the stilling basin. Laboratory measurements of the sequent depth were carried out using three different channel slopes for the rough bed and a single slope for the smooth bed. A solution useful for estimating the sequent depth ratio in a rectangular channel for different relative roughness and bed slope is proposed and positively tested by the present measurements. This solution can also be used to estimate the sequent depth ratio of classical hydraulic jump…

Flume experiments for assessing the dye-tracing technique in rill flows

Abstract Flow velocity controls hillslope soil erosion and is a key hydrodynamic variable involved in sediment transport and deposition processes. The dye-tracer technique is one of the most applied methods for measuring velocity of shallow interrill and rill flow. The technique is based on the injection of a tracer in a specific point and the measurement of its speed to travel the known distance from the injection point to a given channel section. The dye-tracer technique requires that the measured surface flow velocity has to be corrected to obtain the mean flow velocity using a correction factor which is generally empirically deduced. The technique has two sources of uncertainties: i) th…

Slope threshold in rill flow resistance

The applicability of a theoretical rill flow resistance equation, based on the integration of a power velocity distribution, was tested using measurements carried out in mobile and fixed bed rills, shaped on plots having different slopes (9, 14, 15, 18, 22, 24, 25 and 26%) and soil textures (clay fractions ranging from 32.7% to 73% and silt of 19.9–30.9%), and flume measurements available in the literature. The Darcy–Weisbach friction factor resulted dependent on the slope, Froude number, Reynolds number and clay and silt percentages, used as variables representative of soil transportability and detachability, respectively. This theoretical approach was applied to two different databases di…

An automatic approach for rill network extraction to measure rill erosion by terrestrial and low‐cost unmanned aerial vehicle photogrammetry

For an erosion event (October 2016) occurred at the Sparacia experimental area (Southern Italy), both terrestrial and low-altitude aerial surveys were carried out by consumer grade camera and quadcopter (low-cost unmanned aerial vehicle [UAV]) to measure rill erosion on two plots with steepness of 22% and 26%. Applying the structure from motion (SfM) technique, the three-dimensional digital terrain models (3D-DTMs) and the quasi three-dimensional models (2.5D-digital elevation model [DEM]) were obtained by the two surveys. Furthermore, 3D-DTM and DEM were built using the available aerial photographs (166) and adding 40 terrestrial photographs. For the first time, the convergence index was a…

Criteri di dimensionamento delle rampe in pietrame

Theoretical prediction of rainfall intensity for a small rainfall simulator

In this contribution, a theoretical approach was developed for predicting rainfall intensity for a small rainfall simulator. The developed equation was tested for two different devices and different pressure head and water temperature values. The proposed relationship was found to have a good predictive ability of rainfall intensity. The proposed theoretical approach could be usable with other devices that operate on the same principles of the simulator considered in this investigation.

Closure to Discussion on “Sequent depth ratio of a B- jump” by Ohtsu and Yasuda

Una nuova formulazione del risalto idraulico

EFFETTI DELLA PENDENZA PARCELLARE SULLA PERDITA DI SUOLO STIMATA CON LA USLE-MM

La USLE-MM è un modello previsionale della perdita di suolo alla scala dell’evento erosivo che introduce il coefficiente di deflusso parcellare nel set di variabili indipendenti della USLE e consente la previsione di una perdita di suolo per unità di superficie non necessariamente crescente con la lunghezza della pendice. Tale circostanza, che la USLE non è in grado di riprodurre, è stata ampiamente riscontrata in letteratura e nell’area sperimentale di Sparacia. Il fattore climatico della USLE-MM è pari ad una potenza del prodotto del coefficiente di deflusso per l’indice di aggressività della pioggia di Wischmeier e Smith (1978). Il modello USLE–MM è stato originariamente dedotto facendo …

Testing assumptions and procedures to empirically predict bare plot soil loss in a Mediterranean environment

Empirical prediction of soil erosion has both scientific and practical importance. This investigation tested USLE and USLE-based procedures to predict bare plot soil loss at the Sparacia area, in Sicily. Event soil loss per unit area, Ae, did not vary appreciably with plot length, λ, because the decrease in runoff with λ was offset by an increase in sediment concentration. Slope steepness, s, had a positive effective on Ae, and this result was associated with a runoff coefficient that did not vary appreciably with s and a sediment concentration generally increasing with s. Plot steepness did not have a statistically detectable effect on the calculations of the soil erodibility factor of bot…

Briglie con savanella a profilo W

Testing a new rill flow resistance approach using the Water Erosion Prediction Project experimental database

In this paper, a recently theoretically deduced rill flow resistance equation, based on a power‐velocity profile, was tested using the Water Erosion Prediction Project database. This database includes measurements of flow velocity, water depth, cross section area, wetted perimeter, and bed slope that were made in rills shaped on experimental sites distributed across the continental United States. In particular, three different experimental conditions (only rainfall, only flow, and rain with flow) were examined, and for each condition, the theoretically based relationship for estimating the Γ function of the power velocity profile was calibrated. The results established that (a) the Darcy‐We…

Sulla geometria idraulica dei rill e degli ephemeral gully rilevati a Sparacia, in Sicilia

Estimating soil loss of given return period by USLE-M-type models

Many field investigations have clearly shown that rare and severe events control total soil erosion occurring over a long time period with up to 92% of total soil erosion over a 7‐year period resulting from just three daily events. Therefore, soil conservation strategies should be developed taking into account large events rather than long‐term average erosion. From an engineering point of view, establishing the soil loss of a given return period is needed. This can be obtained by the frequency analysis of soil loss measurements or by suitable soil erosion models. The USLE‐M modified and USLE‐M based are two empirical Universal Soil Loss Equation‐Modified (USLE‐M) type models which were dev…

Valutazione delle altezze coniugate per un risalto idraulico tipo B-jump

Measuring the USLE soil erodibility factor in the unit plots of Sparacia (southern Italy) experimental area

The Universal Soil Loss Equation (USLE) is still widely used to predict soil loss by water erosion and to establish soil conservation measures. In this model, the soil erodibility factor K accounts for the susceptibility of the soil to be eroded due to the detachment and transport processes operated by the erosive agents. According to the USLE scheme, the K factor should be measured on unit plots, i.e., bare plots of given length (22 m) and steepness (9%) tilled along the maximum slope direction, but there is little evidence that there ever existed an actual unit plot between the plots used to develop the USLE. Given the difficulty in collecting sufficient data to adequately measure K, the …

Measuring rill erosion at plot scale by a drone-based technology

The traditional direct method (i.e. metric ruler and rillmeter) of monitoring rill erosion at plot scale is time consuming and invasive since it modifies the surface of the rilled area. Measuring rill features using a drone-based technology is considered a non-invasive method allowing a fast field relief. In the experimental Sparacia area a survey by a quadricopter Microdones md4-200 was carried out and this relief allowed the generation of a Digital Elevation Model (DEM), with a mesh size of 1 cm and a resolution elevation equal to 2 mm, for three plots (L, G and C) affected by rill erosion. At first for the experimental L plot, which is 44 m long, the rill features were surveyed by a “man…

Testing a new sampler for measuring plot soil loss

In order to measure soil loss in equipped plots the estimate of the weight of solid material intercepted at their lower end is required. At the experimental area of Sparacia, Sicily, the runoff produced by an erosive event is collected within storage tanks with a capacity of about 1m3. In this paper, the use of a new sampler is proposed to measure easily the weight of solid material eroded from an experimental plot and collected into a storage tank. The sampler is a cylinder having a closing valve at the bottom. Two different series of runs were carried out both to test the reliability of the sampler and to establish a sampling procedure, respectively. An analysis of various sampling config…

New Expression of the Hydraulic Jump Roller Length

AbstractThis paper presents the results of an experimental investigation on the roller length of both classical and B-jumps on smooth beds. Using the measurements conducted in this investigation and those available in the literature, a new relationship is proposed for estimating the roller length of classical and B-jumps on smooth beds. Finally, it is demonstrated that the proposed equation is also applicable to estimate the roller length of hydraulic jumps on rough horizontal beds.

UN NUOVO MODELLO PER LA STIMA DELL’ERODIBILITÀ RILL

Molti modelli process-oriented per la previsione dell’erosione rill utilizzano parametri, come l’erodibilità rill, che sono specifici del sito di interesse e pertanto l’applicazione dei suddetti modelli necessita la misura di questi parametri o una loro stima indiretta. L’obiettivo del presente lavoro è quello di proporre un metodo per la misura indiretta dell’erodibilità rill del suolo dell’area sperimentale di Sparacia, in Sicilia. Sono state utilizzate le misure condotte sui rill rilevati nelle parcelle di Sparacia in occasione di sette eventi di pioggia naturale e un semplice approccio matematico basato sull’equazione che simula il distacco dei sedimenti tenendo conto della variabilità …

La lunghezza del roller del risalto idraulico

Testing the Outflow Process over a Triangular Labyrinth Weir

In this paper, the dimensionless stage-discharge relation for a sharp-crested triangular labyrinth weir, determined in a previous study, is initially tested by some experimental runs carried out in a laboratory flume. According to this relationship, the flow magnification is affected by the length-magnification ratio and the head to one cycle width ratio. The measurements allowed to test the applicability of this dimensionless relation for different values of both the angle of the sidewall to the main flow direction and the weir height. Finally, the proposed dimensionless equation was also tested by using experimental measurements carried out for broad-crested triangular labyrinth weir.

Flow resistance equation for rills

In this paper, a new flow resistance equation for rill flow was deduced applying dimensional analysis and self‐similarity theory. At first, the incomplete self‐similarity hypothesis was used for establishing the flow velocity distribution whose integration gives the theoretical expression of the Darcy–Weisbach friction factor. Then the deduced theoretical resistance equation was tested by some measurements of flow velocity, water depth, cross section area, wetted perimeter, and bed slope carried out in 106 reaches of some rills shaped on an experimental plot. A relationship between the velocity profile, the channel slope, and the flow Froude number was also established. The analysis showed …

VERIFICA DI UNA TECNICA FOTOGRAFICA PER IL RILIEVO DELLA GEOMETRIA DI UN CANALE IN TERRA

Nella memoria sono riportati i risultati delle verifiche di applicabilità di una tecnica image-based per il monitoraggio dei processi di erosione canalizzata. L’indagine, in particolare, ha avuto lo scopo di testare l’uso di modelli tridimensionali del terreno (DTM) ottenuti con l’impiego di un numero elevato di fotografie della stessa scena acquisite da differenti punti di vista (Tecnica “Structure-From Motion” SFM e “Multi-View-Stereo MVS). Il DTM tridimensionale (3D) è stato generato utilizzando il software open source Autodesk 123D Catch mentre per la creazione del Digital Elevation Model DEM (2.5D) è stato impiegato il software CloudCompare. Dei due canali in terra utilizzati nella spe…

Rilievo di un ephemeral gully nell’area sperimentale di Sparacia mediante una tecnica fotografica

Nella memoria sono riportati i risultati dell’applicazione di una tecnica imagebased per il monitoraggio di un ephemeral gully formatosi nel gennaio 2015 nell’area sperimentale di Sparacia. Nel gully, lungo 54 m, sono state individuate 24 sezioni trasversali che sono state rilevate in campo mediante l’uso di un profilometro. L’indagine ha inoltre previsto la realizzazione di un modello tridimensionale del terreno (DTM) ottenuto con l’impiego di un numero elevato di fotografie della stessa scena acquisite da differenti punti di vista (Tecnica “Structure-From Motion” SFM e “Multi-View-Stereo MVS). Dal DTM tridimensionale (3D) e dal modello 2.5D sono stati estratti i profili delle sezioni tras…

Field investigation of rill and ephemeral gully erosion in the Sparacia experimental area, South Italy

Abstract This paper reports the results of a field investigation aiming at characterizing the morphology and hydraulics of both rills and ephemeral gullies (EGs) monitored at Sparacia experimental area, Sicily, Italy. The comparison between rill and interrill erosion measurements showed that sediment delivery processes occurred in some erosive events and that the rill erosion rate was dominant in many cases. The measurements were used for testing both the empirical relationships between the channel (rill, EGs and gully) length and its eroded volume and among the morphological variables (length, width, depth and volume) describing the channelized process. Finally, the rill and EGs hydraulic …

Measurement of Water Soil Erosion at Sparacia Experimental Area (Southern Italy): A Summary of More than Twenty Years of Scientific Activity

The main purpose of this article is to give a general idea of the scientific activity that was carried out starting from the 2000s on the basis of the data collected in the plots installed at the Sparacia experimental station for soil erosion measurement in Sicily, South Italy. The paper includes a presentation of the experimental site, a description of the methods and procedures for measuring soil erosion processes both available in the literature and applied at the Sparacia station (sediment sampling and water level reading in the storage tanks for total erosion measurements; profilometer, and Structure from Motion technique for rill erosion measurements), and the main results obtained in…

Una nuova installazione sperimentale per la misura delle caratteristiche energetiche della precipitazione e della perdita di suolo parcellare

Studio sperimentale del risalto idraulico per differenti condizioni di pendenza e scabrezza del fondo

L’attività di ricerca svolta nel corso dei tre anni del Dottorato di Ricerca in Idronomia Ambientale ha riguardato lo studio sperimentale del risalto idraulico e, più specificatamente, delle grandezze che ne definiscono la geometria, vale a dire le altezze coniugate e la lunghezza del roller. In particolare l’attività di ricerca è stata incentrata sullo studio, alla scala di laboratorio, del risalto su fondo scabro e di quello denominato B-jump. Dopo una prima fase di studio della letteratura scientifica pertinente, l’indagine è stata orientata alla verifica, sulla base delle misure sperimentali condotte e dei dati di altri Autori, delle relazioni esistenti in letteratura per la stima sia d…

Modellazione della produzione di sedimenti nel bacino sperimentale SPA2 in Sicilia

Hydraulic jumps on rough beds

This paper presents the results of an experimental investigation on the hydraulic jump on horizontal rough beds. Experiments were carried out to study the effect of bed roughness on both the sequent depth ratio and the roller length. The investigation allowed the writers to positively test the reliability of a new solution of the momentum equation for the sequent depth ratio as a function of the Froude number and the ratio between the roughness height and the upstream supercritical flow depth. The applicability of some empirical relationships for estimating the roller length was also tested.